A method of wet laying short fiber insulation batt

Abstract

The application discloses a kind of short fiber insulation felt methods for preparing by wet process, short carbon fiber is laid into uniform mesh tire unit by airflow carding technology, after weighing, resin glue solution is sprayed on the surface of mesh tire and is conveyed to the pre-curing of baking tunnel;Using the mold of track reciprocating motion alternately receives the pre-cured mesh tire of conveying belt and the mesh tire unit of new laying machine, new laying mesh tire unit needs to be weighed, sprayed and pre-cured, and after multiple cycles, the dense multi-layer mesh tire structure with controllable layer number is formed;After the mold loaded with multi-layer mesh tire is hot-pressed and cured, the obtained blank is treated at high temperature in a graphitization furnace under inert gas or vacuum protection, and short fiber insulation felt is prepared.The method significantly improves the resin infiltration uniformity and structural density of the insulation felt through the synergistic optimization of resin infiltration and multi-layer laying process, the product density and thermal insulation performance are stable, and it is suitable for continuous production process, and has industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials, and specifically to a method for wet-process preparation of short fiber thermal insulation felt. Background Technology

[0002] Carbon fiber insulation felt is a lightweight, high-porosity thermal insulation material made primarily of carbon fiber through specific processes. It possesses excellent high-temperature stability, low thermal conductivity, chemical corrosion resistance, and good mechanical flexibility. Due to its good thermal shielding, thermal shock resistance, and chemical inertness, carbon fiber insulation felt is widely used in the design of thermal insulation layers for high-temperature furnaces in fields such as the high-temperature synthesis and crystal growth (e.g., physical vapor transport and chemical vapor deposition) of SiC (silicon carbide) and silicon-based raw materials (e.g., polycrystalline silicon and monocrystalline silicon).

[0003] Currently, the mainstream preparation methods for carbon fiber insulation felt include needle punching, wet forming, and chemical vapor deposition (CVD) reinforcement. Needle punching involves cross-linking short-cut carbon fibers into felt through a needle punching process. This method is low-cost and efficient, but the randomness of fiber orientation leads to uneven density distribution in the felt, making it prone to localized shrinkage and deformation at high temperatures, affecting the consistency of thermal insulation performance. CVD reinforcement involves depositing a pyrolytic carbon or SiC coating on the surface of the carbon fiber felt. While this method can produce high-temperature-resistant insulation felt, it is complex, costly, and excessively thick coatings can cause the felt to become brittle, limiting its flexible applications. Wet forming uses a liquid (water or organic solvent) as the dispersion medium, preparing the felt through the flow, deposition, and solidification of a fiber suspension. This method is widely used due to its advantages such as high formability, good surface quality of the prepared felt, uniform fiber distribution, ability to produce complex shapes, and high material utilization. For example, patent CN106336236A discloses a method for preparing carbon fiber insulation materials using a short fiber wet molding process. While the carbon fiber composite material prepared by this method has a low thermal conductivity, the surface smoothness is poor. Furthermore, due to stress, a large amount of resin deposits on the bottom surface of the preform during the fiber and resin mixing and filtration process, leading to surface cracking during the carbonization and graphitization stage due to excessive resin content and untimely stress release. To address the problem of easy surface cracking in insulation materials, patent CN 110002888A proposes a method for preparing short fiber preforms using vacuum suction. This method impregnates the preform with resin. While the insulation felt prepared using this method has good smoothness and is less prone to surface cracking, it suffers from uneven resin distribution within the product, resulting in unstable product performance. Summary of the Invention

[0004] [Technical Issues]

[0005] Existing wet processing methods suffer from uneven resin distribution within the product, leading to unstable product performance.

[0006] [Technical Solution]

[0007] To address the aforementioned problems, the present invention aims to provide a method for wet-process preparation of short-fiber thermal insulation felt. In the production process of short-fiber thermal insulation felt, firstly, air-flow combing technology is used to create mesh units. Then, the mesh units are sprayed with adhesive and subsequently conveyed to a drying tunnel for pre-curing. After the pre-curing stage, the pre-cured mesh units are transported to a mold at the exit of the conveying device using the same conveying device. Thereafter, the predetermined process of air-flow combing, adhesive spraying, and pre-curing is continuously repeated. Once a multi-layer mesh structure is formed within the mold, the entire mold is placed in a hot press for heat curing. The preform after hot pressing curing is then subjected to graphitization treatment to finally obtain the short-fiber thermal insulation felt product. This invention involves spraying resin onto the surface of the bottommost mesh unit and then laying new pre-cured mesh units on the surface of the pre-cured mesh unit to create a multi-layer mesh structure. The amount of resin sprayed is adjusted in real time according to the weight of the mesh. The resulting insulation felt has high resin wetting, uniform mesh laying, and uniform and stable product density and insulation performance. Furthermore, this invention's method is beneficial for continuous production.

[0008] To achieve the above objectives, the present invention first provides a method for wet-process preparation of short fiber thermal insulation felt, comprising the following steps:

[0009] S1. Airflow web formation: Short carbon fibers are combed through an airflow combing machine to form a web of uniform thickness, thus obtaining a web unit;

[0010] S2. Weighing of the mesh tire: A belt scale is installed at the outlet of the air blower to weigh the mesh tire unit in real time.

[0011] S3. Resin impregnation: A nozzle is set above the mesh unit to spray resin liquid according to the weight of the mesh, and the resin liquid is sprayed onto the surface of the mesh to obtain a resin-impregnated mesh.

[0012] S4. Resin pre-curing: The resin-impregnated mesh obtained in step S3 is conveyed into the drying tunnel through a conveying device to pre-cur the resin and obtain a pre-cured mesh.

[0013] S5. Mold installation: Place the mold on the track at the exit of the conveyor device and make it reciprocate back and forth on the track;

[0014] S6. Multi-layer mesh laying: The pre-cured mesh is fed into the mold that is making reciprocating linear motion via a conveyor. When the mold moves to the outlet of the conveyor, with the cooperation of the air combing machine and the conveyor, the new pre-cured mesh unit will be evenly laid on the surface of the pre-cured mesh in the mold. Then, the mold returns to the discharge end of the conveyor to receive the new pre-cured mesh, and repeats steps S2 to S4. After multiple rounds of operation, the mesh layers are stacked in an orderly manner, and finally a multi-layer mesh with a dense structure and controllable number of layers is obtained.

[0015] S7. Blank forming: Place the mold carrying the multi-layer mesh in step S6 into a hot press for heating and pressure curing to obtain the cured blank.

[0016] S8. Graphitization of the blank: The cured blank obtained in step S7 is placed in a graphitization furnace under the protection of inert gas or vacuum for high-temperature treatment to obtain short fiber thermal insulation felt.

[0017] In one embodiment of the present invention, the short carbon fiber includes any one of pitch-based, PAN-based, viscose-based, and phenolic short fibers, and the length of the carbon fiber is 3-8 mm.

[0018] In one embodiment of the present invention, the thickness of the mesh tire unit in step S1 is 3-10 mm.

[0019] In one embodiment of the present invention, the areal density of the mesh unit in step S1 is 30-150 g / m². 2 .

[0020] In one embodiment of the present invention, the mass ratio of the mesh weight to the resin liquid in step S3 is 1:(2-8).

[0021] In one embodiment of the present invention, the resin liquid in step S3 includes 1 part of binder, 2-10 parts of solvent, 0.02-0.05 parts of flame retardant, and 0.05-0.1 parts of surfactant.

[0022] In one embodiment of the present invention, the adhesive includes at least one of epoxy resin, phenolic resin, and furfuryl ketone resin.

[0023] In one embodiment of the present invention, the solvent is water or ethanol.

[0024] In one embodiment of the present invention, the flame retardant includes at least one of ammonium chloride, ammonium sulfate, and melamine cyanurate (MCA).

[0025] In one embodiment of the present invention, the surfactant includes at least one of KH560, sodium dodecyl sulfate, and sulfated castor oil.

[0026] In one embodiment of the present invention, the multi-layered mesh tire refers to a structure composed of 6 to 10 mesh tire units.

[0027] In one embodiment of the present invention, the pre-curing temperature in step S4 is 80-100°C and the pre-curing time is 5-10 min.

[0028] In one embodiment of the present invention, the width of the mesh tire is the same as the width of the mold, and the reciprocating distance of the mold is the same as the width of the mold.

[0029] In one embodiment of the present invention, the pressure of the hot press during operation in step S7 is 0.1 MPa-1 MPa.

[0030] In one embodiment of the present invention, the curing temperature in step S7 is 150-300℃ and the curing time is 10-20h.

[0031] In one embodiment of the present invention, the inert gas mentioned in step S8 is nitrogen or argon.

[0032] In one embodiment of the present invention, the vacuum degree of the vacuum in step S8 is 5-20 mbar.

[0033] In one embodiment of the present invention, the high temperature treatment in step S8 is 1800℃-2600℃, and the high temperature treatment time is 10-24h.

[0034] The present invention also provides a short fiber thermal insulation felt prepared according to the above method.

[0035] Beneficial effects:

[0036] 1. This invention involves setting a mold on a track at the exit of a conveyor device, allowing the mold to move back and forth in a straight line. The mold carrying the pre-cured mesh can return to the exit of the conveyor device to receive new pre-cured mesh. After repeated operation, a mesh structure with 6-10 layers is formed. This multi-layered mesh is then hot-pressed and graphitized to obtain a multi-layered insulation felt. The insulation felt prepared using this method has uniform layers, stable product density, and high insulation efficiency. Furthermore, this method eliminates the need for manual stacking of multiple layers, allows for continuous production, and has high forming efficiency.

[0037] 2. In this invention, short fiber airflow is first laid into a mesh structure. A belt scale is set after the airflow machine. The weight of the mesh is fed back in real time by the belt scale to adjust the amount of adhesive sprayed, so that the resin liquid in the mesh is evenly impregnated, which greatly reduces the thermal conductivity of the insulation felt and improves the insulation performance.

[0038] 3. In this invention, the mesh substrate with sprayed adhesive is first pre-cured, and then the pre-cured mesh substrate is laid to form a multi-layer mesh structure of 6 to 10 layers. Finally, the mesh substrate is hot-pressed and graphitized to prepare thermal insulation felt. The thermal insulation felt prepared by this invention has good thermal insulation performance and a thermal conductivity as low as 0.035 W / (m·K). Attached Figure Description

[0039] Figure 1 The diagram shows the apparatus for preparing the thermal insulation felt of the present invention, in which 1 is a hopper, 2 is an airflow combing machine, 3 is a belt scale, 4 is a nozzle, 5 is a conveyor belt, 6 is a drying tunnel, 7 is a track, 8 is a mold, and 9 is a mesh.

[0040] Figure 2 This is a schematic diagram of the manufacturing process of the thermal insulation felt of the present invention. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0042] Resin wetting uniformity test:

[0043] Interlayer wetting uniformity test: The interlayer area is observed using an optical microscope or an electron microscope to directly check the degree of resin wetting of the fiber, whether there are unwetted areas or resin enrichment / depletion phenomena.

[0044] Local wetting uniformity test: Directly observe the bonding state between fibers and resin in local areas, such as whether there are local defects such as unwetting of monofilaments or resin agglomeration.

[0045] Example 1

[0046] A method for wet-process preparation of short fiber thermal insulation felt includes the following steps:

[0047] S1. Airflow web formation: Short-fiber carbon fibers (pitch-based) are combed through an airflow combing machine 2 to form a uniformly thick web, resulting in a web unit with a weight of 9g, a thickness of 3mm, and an areal density of 100g / m³. 2 .

[0048] S2, Mesh tire weighing: A belt scale 3 is installed at the airflow outlet to weigh the mesh tire unit in real time;

[0049] S3. Resin impregnation: A nozzle 4 is set above the mesh, and the resin liquid is sprayed onto the surface of the mesh according to the weight of the mesh and the resin liquid (1:4) to obtain the mesh after resin impregnation; the resin liquid includes 1 part of phenolic resin, 2 parts of ethanol, 0.02 parts of flame retardant MCA, and 0.05 parts of surface activator KH560.

[0050] S4. Resin pre-curing: The resin-impregnated mesh obtained in step S3 is conveyed into the drying tunnel 6 via conveyor belt 5, and the resin is pre-cured at 80°C for 10 minutes to obtain the pre-cured mesh 9.

[0051] S5. Mold installation: Place the mold on track 7 and make it reciprocate back and forth on track 7;

[0052] S6. Reciprocating Net Laying: The pre-cured net 9 is fed into the mold 8, which is making reciprocating linear motion, via the conveyor belt 5. When the mold 8 moves to below the outlet of the conveyor belt 5, with the cooperation of the air combing machine 2 and the conveyor belt 5, the new pre-cured net unit 9 will be evenly laid on the surface of the pre-cured net in the mold 8. Then, the mold 8 returns to the discharge end of the conveyor belt 5 to receive the new pre-cured net, and repeats steps S2 to S4. After multiple rounds of operation, the net layers are stacked in an orderly manner, and finally a 6-layer net with a dense structure and controllable number of layers is obtained.

[0053] S7. Blank forming: Place the mold 8 that carries the 6 layers of mesh in step S6 into a hot press for heating and pressure curing to obtain the cured blank; the curing temperature is 180℃, the pressure is 0.1Mpa, and the time is 18h.

[0054] S8. Graphitization of the blank: The cured blank obtained in step S7 is placed in a graphitization furnace, heated to 2000℃, calcined for 10 hours under nitrogen protection, and cooled to room temperature to obtain short fiber thermal insulation felt.

[0055] Example 2

[0056] The difference between Example 2 and Example 1 is that the mass ratio of the mesh to the resin liquid in step S3 is 1:2.

[0057] Example 3

[0058] The difference between Example 3 and Example 1 is that the resin solution used in step S3 includes 1 part phenolic resin, 4 parts ethanol, 0.03 parts flame retardant MCA, and 0.06 parts surfactant KH560.

[0059] Example 4

[0060] The difference between Example 4 and Example 1 is that the resin solution used in step S3 includes 1 part phenolic resin, 6 parts ethanol, 0.04 parts flame retardant MCA, and 0.07 parts surfactant KH560.

[0061] Example 5

[0062] The difference between Example 5 and Example 1 is that the number of layers of the mesh tire is adjusted to 12.

[0063] Comparative Example 1

[0064] A method for wet-process preparation of short fiber thermal insulation felt includes the following steps:

[0065] S1. Air-laid web: Short-fiber carbon fibers (pitch-based) are combed by an air-flow combing machine and then conveyed to a web-laying machine to form a web of uniform thickness, resulting in a web unit; its weight is 9g, its thickness is 3mm, and its areal density is 100g / m³. 2 .

[0066] S2. Stack the 6 mesh units obtained in step S1 together to obtain 6 layers of mesh.

[0067] S3. Resin impregnation: A nozzle is set above the mesh to spray 216g of resin liquid onto the surface of the mesh, resulting in a resin-impregnated mesh; the resin liquid includes 1 part phenolic resin, 2 parts ethanol, 0.02 parts flame retardant MCA, and 0.05 parts surface activator KH560.

[0068] S4. Vacuum suction: Under vacuum conditions, the resin from step S3 is suctioned into the interior of the mesh.

[0069] S5. Blank forming: The 6-layer mesh obtained in step S4 is placed in a hot press and heated and pressed to cure, resulting in a cured blank. The curing temperature is 180℃, the pressure is 0.1Mpa, and the time is 18h.

[0070] S6. Graphitization of the blank: The cured blank obtained in step S5 is placed in a graphitization furnace, heated to 2000℃, calcined for 10 hours under nitrogen protection, and cooled to room temperature to obtain short fiber thermal insulation felt.

[0071] Comparative Example 2

[0072] A method for wet-process preparation of short fiber thermal insulation felt includes the following steps:

[0073] S1. Air-laid web: Short-fiber carbon fibers (pitch-based) are combed by an air-flow combing machine and then conveyed to a web-laying machine to form a web of uniform thickness, resulting in a web unit; its weight is 9g, its thickness is 3mm, and its areal density is 100g / m³. 2 .

[0074] S2. Resin impregnation: A nozzle is set above the mesh to spray 36g of resin liquid onto the surface of the mesh, resulting in a resin-impregnated mesh; the resin liquid includes 1 part phenolic resin, 2 parts ethanol, 0.02 parts flame retardant MCA, and 0.05 parts surface activator KH560.

[0075] S3. Resin pre-curing: The resin-impregnated mesh obtained in step S2 is conveyed into the drying tunnel through a conveying device, and the resin is pre-cured at 80°C for 10 minutes to obtain the pre-cured mesh.

[0076] S4. Mold installation: Place the mold on the track and make it reciprocate back and forth on the track;

[0077] S5. Reciprocating Net Laying: The pre-cured net is fed into the mold that is making reciprocating linear motion via a conveyor. When the mold moves to the outlet of the conveyor, with the cooperation of the air combing machine and the conveyor, the new pre-cured net unit will be evenly laid on the surface of the pre-cured net in the mold. Then, the mold returns to the discharge end of the conveyor to receive the new pre-cured net, and repeats steps S2 to S4. After multiple rounds of operation, the net layers are stacked in an orderly manner, and finally a 6-layer net with a dense structure and controllable number of layers is obtained.

[0078] S6. Blank forming: The mold carrying the 6-layer mesh in step S5 is placed in a hot press for heating and pressure curing to obtain the cured blank; the curing temperature is 180℃, the pressure is 0.1Mpa, and the time is 18h.

[0079] S7. Graphitization of the blank: The cured blank obtained in step S6 is placed in a graphitization furnace, heated to 2000℃, calcined for 10 hours under nitrogen protection, and cooled to room temperature to obtain short fiber thermal insulation felt.

[0080] Comparative Example 3

[0081] The difference between Comparative Example 3 and Example 1 is that the number of mesh layers was adjusted to 4.

[0082] Comparative Example 4

[0083] The difference between Comparative Example 4 and Example 1 is that the ratio of mesh weight to resin liquid was adjusted to 1:10.

[0084] Comparative Example 5

[0085] The difference between Comparative Example 5 and Example 1 is that the resin solution does not contain surfactants.

[0086] Comparative Example 6

[0087] The difference between Comparative Example 6 and Example 1 is that the resin solution does not contain flame retardants.

[0088] Table 1 Comparison of various performance parameters of thermal insulation felt

[0089] name Uniformity of resin impregnation Number of mesh tire layers Density (g / cm³) Thermal conductivity (W / (m·K)) Thermal insulation performance Machinability Example 1 Interlayer wetting rate ≥95% 6 0.17 0.035 excellent excellent Example 2 Interlayer wetting rate ≥90% 6 0.1 0.038 middle Difference Example 3 Interlayer wetting rate ≥94% 6 0.17 0.036 good good Example 4 Interlayer wetting rate ≥93% 6 0.17 0.037 good good Example 5 Interlayer wettability ≥92% 12 0.17 0.04 middle middle Comparative Example 1 Local infiltration rate 85% 6 0.16 0.038 middle Difference Comparative Example 2 Local infiltration rate 70% 6 0.15~0.18 0.042 Difference Difference Comparative Example 3 Interlayer wetting rate ≥90% 4 0.13 0.04 middle Difference Comparative Example 4 Local infiltration rate 80% 6 0.22 0.045 Difference Difference Comparative Example 5 Interlayer wetting rate 80% 6 0.17 0.039 middle middle Comparative Example 6 Interlayer wetting rate ≥93% 6 0.17 0.038 middle middle

[0090] Table 1 shows the performance test results of the thermal insulation felts in Examples 1-5 and Comparative Examples 1-6. As can be seen from Table 1, the thermal insulation felt in Example 1 exhibits the best performance. Examples 3 and 4, based on Example 1, changed the composition and proportion of the resin adhesive, resulting in a slight decrease in the performance of the thermal insulation felt, but the insulation effect remained good. Comparative Examples 5 and 6 omitted the addition of surfactants and flame retardants, respectively, leading to a decrease in the insulation effect of the thermal insulation felt. This indicates that surfactants and flame retardants in the resin adhesive have a significant impact on the insulation performance of the thermal insulation felt. Example 2, based on Example 1, reduced the spraying ratio of the resin adhesive, resulting in poor resin wetting and wetting uniformity, thus leading to a decrease in the insulation effect of the thermal insulation felt and relatively poor processability. Comparative Example 4 increased the amount of resin adhesive sprayed compared to Example 1, resulting in a local wetting rate of 80% in the insulation felt and a significant decrease in insulation effect. This indicates that the amount of resin adhesive sprayed has a significant impact on the insulation effect of the insulation felt. The maximum amount of resin adhesive sprayed should not exceed 8 times the weight of the insulation felt. Excessive spraying will lead to uneven wetting of the resin adhesive, resulting in a decrease in the insulation effect of the insulation felt and a significant decrease in the processability of the insulation felt. In Example 5 and Comparative Example 3, increasing and decreasing the number of mesh layers respectively resulted in an increase in the thermal conductivity of the insulation felt and a decrease in its insulation performance. This may be because if the number of layers is too high, the mesh is over-compacted, leading to a higher density. High density reduces the air pores between fibers and may also cause resin buildup that blocks the pores. The heat conduction path changes from "fiber-air-resin composite conduction" to "fiber-resin direct conduction," increasing the thermal conductivity and deteriorating the insulation performance. If the number of layers is too low, the mesh density is too low. Low density results in insufficient support between fibers, easily forming a large number of fiber contact points (thermal bridges). The proportion of heat conduction through direct fiber transfer increases, leading to an increase in thermal conductivity and a decrease in insulation performance.

[0091] Furthermore, the experimental data from Example 1 and Comparative Example 2 show that if a belt scale is not installed at the outlet of the air blower to adjust the spraying amount in real time according to the weight of the belt scale, the uniformity of resin impregnation in the insulation felt will also be poor, and the density of the insulation felt will be very uneven, resulting in a significant decrease in the effectiveness of the insulation felt.

[0092] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for wet-process preparation of short fiber thermal insulation felt, characterized in that, The thermal insulation felt is continuously prepared according to the following process: air-flow mesh laying → mesh weighing → resin impregnation → resin pre-curing → mold installation → multi-layer mesh laying → blank forming → blank graphitization. The air-laid web machine is equipped with a weighing device at its outlet to weigh the web unit in real time. After the short carbon fibers are laid into web units by the air-laid web machine, during the resin impregnation step, the nozzles above the conveying device that transports the web units spray resin adhesive according to the weight of the web units to impregnate the web. The mass ratio of the sprayed resin adhesive to the web unit is (4-8):

1. The resin adhesive includes 1 part binder, 2-10 parts solvent, 0.02-0.05 parts flame retardant, and 0.05-0.1 parts surfactant. The binder includes at least one of epoxy resin, phenolic resin, and furfuryl ketone resin. The solvent is water or ethanol. The flame retardant includes at least one of ammonium chloride, ammonium sulfate, and melamine cyanurate. The surfactant includes at least one of KH560, sodium dodecyl sulfate, and sulfated castor oil. In the mold installation process, a mold for receiving pre-cured mesh units is set at the outlet of the conveying device. After the mold receives multiple pre-cured mesh units, multi-layer mesh laying is completed. Multi-layer mesh laying refers to laying 6 to 10 layers of mesh units.

2. The method according to claim 1, characterized in that, The short-fiber carbon fiber includes any one of pitch-based, PAN-based, viscose-based, and phenolic short fibers, and the length of the short-fiber carbon fiber is 3-8 mm.

3. The method according to claim 1, characterized in that, The thickness of the mesh unit is 3-10 mm, and the areal density is 30-150 g / m³. 2 .

4. The method according to claim 1, characterized in that, In the resin pre-curing step, the resin-impregnated mesh unit is conveyed to the drying tunnel by a conveying device for pre-curing. The pre-curing temperature is 80-100℃ and the pre-curing time is 5-10 minutes.

5. The method according to claim 1, characterized in that, During the mold installation process, the width of the mold is consistent with the width of the mesh tire, and the distance the mold travels back and forth is consistent with the width of the mold.

6. The method according to claim 1, characterized in that, In the blank forming step, the mold containing the multi-layer mesh unit is placed in a hot press for heating and pressure curing. The pressure of the hot press is 0.1-1MPa, the curing temperature is 150-300℃, and the curing time is 10-20h.

7. The method according to claim 1, characterized in that, In the graphitization step of the billet, graphitization is carried out under the protection of an inert gas or a vacuum, wherein the inert gas is nitrogen or argon, the vacuum degree is 5-20 mbar, the graphitization temperature is 1800-2600℃, and the graphitization time is 10-24h.

8. The short fiber thermal insulation felt prepared by any one of claims 1 to 7.

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